This invention relates to the repair of joints in a body, and more particularly to facilitating the regeneration of articular cartilage in a joint.
The human body has a variety of different joints. These joints comprise two or more bones that have surfaces which articulate with respect to each other. These surfaces are typically called articulating surfaces. However, the articulating surfaces do not physically ride on each other. In a healthy joint, the articulating surfaces are separated by cartilage, commonly called articular cartilage.
A problem arises when the articular cartilage in a joint is damaged because it typically does not regenerate. Articular cartilage can be damaged by diseases such as osteoarthritis, chondromalacia and rheumatoid arthritis. It can also be damaged by fractures which pass through an articular cartilage surface or due to a blow to the joint which causes the articular cartilage to split or causes contusion of the articular cartilage.
When the articular cartilage is damaged, the joint is subjected to increased friction. This causes relatively rapid degeneration of the remaining articular cartilage. This is followed by degenerative changes in the articulating surfaces of the bones in the joint when they become exposed which results in symptoms of pain.
One method of treating the above-described conditions has been to replace the damaged joint with an artificial one. However, this requires a relatively major operation and the resulting trauma to the patient often requires a fairly lengthy recovery. In cases where the bones of the joints remain in relatively good condition, it would be desirable to create a condition within the joint which would facilitate regeneration of the articular cartilage.
As has been mentioned, damaged articular cartilage usually does not regenerate. Studies done by Shands in the early 1930's, and later by Bennett, showed that simple wounding of articular cartilage resulted in a minimal and inadequate healing response. However, if the wound extended through the articular cartilage and into the subchondral bone, there was a healing response. [G. A. Bennett, W. Bauer, "Further Studies Concerning the Repair of Articular Cartilage in Dog Joints," Journal of Bone and Joint Surgery, 17:141-150 (1935); A. R. Shands, "The Regeneration of Hyaline Cartilage in Joints, an Experimental Study," Archives of Surgery, 22:137-179 (1931).
Replacement of shoulder joints with prosthesis devices present a unique problem due to the nature of the shoulder joint. The shoulder joint is a successful anatomic compromise toward motion and away from stability. This is just the opposite compromise from the hip joint. Because of this, the bone structure of the shoulder joint is that of a ball with a very shallow socket (glenoid). Also, because humans do not bear weight on their shoulder, there is no need for the shoulder joint to have a heavy, strongly constructed deep socket such as found in the hip joint. The problem this creates with respect to replacing the shoulder joint with prosthesis devices is that the structure supporting the shallow glenoid socket is too delicate to consistently support the prostheses which have been used to replace the glenoid.
It is therefore an objective of this invention to facilitate regeneration of damaged articular cartilage by providing a favorable environment in which regeneration can take place.
It is an objective of this invention to facilitate regeneration of damaged articular cartilage by keeping separated the articulating surfaces of the joint during the time when the articular cartilage is regenerating.
It is also an object of this invention to provide a glenoid "prosthesis" for a shoulder joint by implanting a plurality of domed spacers in the natural glenoid to bear the load applied by the humeral head of a humerus.
According to the method and apparatus of this invention, regeneration of damaged articular cartilage is facilitated by placing one or more spacers between the articulating surfaces of the joint. The spacers are left in place while the articular cartilage regenerates. The spacers prevent the articulating surfaces from rubbing against each other and the articular cartilage can regenerate in the space between the articulating surfaces. A spacer formed in accordance with this invention has a head with a shaft extending therefrom. The shaft is inserted into one of the articulating surfaces so that the head is disposed between the articulating surfaces and keeps them separated while the articular surface regenerates.
Spacers formed in accordance with this invention can be used as a glenoid "prosthesis" in a shoulder joint. A plurality of such spacers, illustratively four, are implanted in the natural glenoid of a shoulder joint. These spacers bear the load of the humeral head of a humerus. These spacers preferably have domed heads.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.